1. Field of the Invention
This invention relates to outlet valves for vessels containing molten material, e.g. metal or glass. More particularly, although not exclusively, the invention relates to such outlet valves for use in tundishes and ladies arranged for the pouring of metal e.g. steel into continuous casting moulds or ingot moulds.
2. Description of the Prior Art
Hitherto, flow control of molten metal, such as steel, from tundishes into continuous casting molds has commonly been accomplished by one of a limited number of methods. Thus, open-metering nozzles have been used having a pre-determined and critical internal bore diameter as the controlling factor for flow rates. Such nozzles have disadvantages in that firstly they cannot cope with aluminum steels, for example, which have a significant tendency to deposit non-metallic occulusions in flow locations typified by such nozzles, secondly any wear in the critical bore of the nozzle leads to an increasing speed of flow which can soon become too fast for continuous casting conditions, thirdly there is a tendency for the nozzle to freeze at start-up, or to suffer clogging when casting low oxygen steel, or when the steel temperature generally approaches liquidus. Fourthly they tend to be difficult to operate with submerged pouring tubes attached below the metering nozzle.
Alternatively, steel flow has been controlled by the use of stopper rods introduced from above and intended to block the outlet nozzles. Disadvantages of such stopper rods are firstly that they require precise setting and are difficult to adjust to ensure precise control at the start of the cast, and secondly "Skull" formation on the stopper tip or nozzle seating, especially at the start can prevent shut-off, frequently leading to loss of control and overflow in the casting mold, particularly in billet-bloom machines having a relatively small mold capacity. Thirdly, reliability over long sequences is poor.
Another alternative for controlling steel flow has been by means of sliding gates. Although these have been found to be much more reliable than stopper rods, in shutting off, they may not re-open once closed. Indeed, even throttling a steel flow in tundish vessels is sufficient to encourage freezing and blockage debris is in the bores of the gate system. They suffer from the disadvantages that they are expensive, they are heavy, cumbersome and complicated, they require precise setting and careful maintenance by engineering-type personnel, and they are expensive in operating costs.
It has also been proposed to provide an outle valve in the base of a metal containing vessel comprising an annular valve member spring urged from below the vessel into an annular through formed in the inner lining of the base, the edge of the valve member being rotatable from below to move the notch into and out of registry with a vessel outlet opening from the trough through the base.
This latter arrangement suffers from a number of disadvantages. Thus, the linkage through the base for the spring urging mechanism inevitably involves leakage problems with risk of air ingress and/or steel freezing. No vertical misalignment of the valve member can be tolerated and the disposition of the valve mechanism below the vessel means that any break out could be very damaging. Still further, the notch and outlet will seriously wear during teeming, thus resulting in inadequate closure and subsequent freezing.
It is an object of the present invention to provide an outlet valve for metal containing vessels which overcomes or at least substantially reduces the above mentioned problems and disadvantages.